Non-aqueous secondary batteries (hereinafter, also referred to simply as “secondary batteries”), such as lithium ion secondary batteries, have characteristics such as compact size, light weight, high energy density, and the ability to be repeatedly charged and discharged, and are used in a wide variety of applications. A secondary battery generally includes battery members such as electrodes (positive and negative electrodes) including electrode mixed material layers and a separator that isolates the positive electrode and the negative electrode from one another and prevents short circuiting between the positive and negative electrodes. In recent years, it has become common to use battery members including functional layers such as a porous membrane layer for improving heat resistance and strength or an adhesive layer for improving adhesiveness between battery members.
A binder that displays binding capacity may be used with an objective of binding components in a battery member such as described above, binding battery members to one another, or the like. Moreover, attempts have been made to improve binders used in the formation of electrode mixed material layers and functional layers with the aim of further improving secondary battery performance (for example, refer to PTL 1 and 2).
PTL 1 proposes a technique for inhibiting gas generation caused by halide ions or the like in an electrolysis solution by forming a porous membrane layer using, as a binder, a water-soluble polymer including an acid group-containing monomer unit in a proportion of 20 wt % to 80 wt % and an amide monomer unit in a proportion of 0.1 wt % to 10 wt %.
PTL 2 proposes a technique for inhibiting the formation of aggregates and improving electrical characteristics of a secondary battery by forming a positive electrode mixed material layer using a binder composition for a positive electrode containing: a binder that includes an acidic group-containing ethylenically unsaturated monomer unit in a proportion of 10 mass % to 35 mass % and has a specific weight average molecular weight; an organic dispersion medium; and a specific number of equivalents of lithium relative to acidic groups in the binder.